Recursion Pascal's Triangle (Python)

Question

I'm not sure what I'm doing wrong with my code here in getting a recursive pascal's triangle to work in python. Any help is kindly appreciated :)

n = 5
def printPascal(n):
    Pascal_List = []
    if n == 0:
        Pascal_List.append([1])
        return Pascal_List
    if n == 1:
        Pascal_List.append([1])
        Pascal_List.append([1,1])
        return Pascal_List


    else:

        new_row = [1]
        final_r = printPascal(n - 1)
        last_row = final_r[-1]
        for k in range(1, last_row[-1]):
            new_row.append(final_r[k] + final_r[k - 1])

        new_row += last_row
        final_r.append(new_row)
        return final_r

print(printPascal(n))

Answer 1

You've made a few confusions in the loop that builds a new line. range(1, last_row[-1]) doesn't really make sense; you want to iterate over the indices of the last row, ie range(len(last_row)). You've also mixed up final_r and last_row on the next line.

Here is a corrected version of your code :

n = 5

def printPascal(n):
    Pascal_List = []
    if n == 0:
        Pascal_List.append([1])
        return Pascal_List

    if n == 1:
        Pascal_List.append([1])
        Pascal_List.append([1,1])
        return Pascal_List

    else:
        new_row = [1]
        final_r = printPascal(n - 1)
        last_row = final_r[-1]
        for k in range(len(last_row)-1):
            new_row.append(last_row[k] + last_row[k + 1])
        new_row.append(1)

        final_r.append(new_row)
        return final_r

print(printPascal(n))